Hydrogen firing at elevated temperatures to change the color of glasses whose compositions contain reducible ions is well known. A notable commercial application of that technique is found in the Corning Incorporated eyewear product lines marketed under the SERENGETI.RTM. and CPF.RTM. trademarks. Another example of the effect of hydrogen firing on color is the formation of a black color on glass, used for STEUBEN.RTM. ware or on certain glazed dinnerware products. The color changes induced are attributed to the reduction of a portion of the silver and lead ions, respectively, in the glass to the atomic state.
It is known that a chemical reaction proceeds very fast relative to hydrogen diffusion which leads to the condition of a sharp boundary between the reduced region near the surface, and the unreduced region below the surface. Coloration derives from the reduced layer. Accordingly, it is the object of the present invention to provide a method of forming coloration in desired areas near a glass surface using a barrier film.